Ignoring them makes reading the threads a bit easier but having said that if they are quoted by others then their nonsense might catch my eye.
On the odd occasion I might have reversed the ignore to take a look here and there to see if they beginning to post sensibly before being unsurprised and simply ignoring them again but: I already have put several of the lemmings and more on ignore..

If the lemmings want to yell out "I told you so!" after they've already jumped off the cliff, just put them on ignore.